Research On Lithium Ion Power Battery Management System For Electric Vehicle

Since the second half of the 20th century,the oil crisis and environmental pollution has highlighted.In this situation,the new energy vehicles,especially electric vehicles return to the people's vision,getting the high concern of automobile manufacturers at home and abroad,especially interiorly electric vehicle gain more promotion and greater attention.Battery management system(BMS)is an important part of electric vehicles,the effective management and control of power batteries ensure the efficient use of batteries and driving safety.At present,BMS is still in development stage,and many key technologies are not mature.The emphasis and difficulty of the research is how to improve the battery state of charge(SOC)estimation accuracy and balance between the batteries.In this paper,Ni Co Mn three element lithium battery was chosen as the research objects to study about the battery performance model to estimate SOC and active equalization.In order to obtain accurate current and voltage data,the electric vehicle under study was fully discharged to mark the cell with the lowest capacity.After charging the electric vehicle,the vehicle was run in the complex operating conditions of the city streets,and current,voltage and temperature and a series data of marked cell were collected.The relationship between the open circuit voltage(OCV)of the battery and SOC was measured,and the relationship between OCV and SOC was fitted by built-in function of Matlab.Comparing the advantages and disadvantage of various models of battery.The first-order RC model and the second-order RC model were selected.Combined with the collected data the parameters such as the resistance,capacitance of the selected model were identified by the forgetting factor least squares recursive algorithm.After a period of iterative calculation,the parameter values of the selected model can be effectively identified,and the results were stable.According to the value of the identified parameter was verified by the terminal voltage as the verification value.The verification results showed that the identified parameters are accurate.Comparing the various methods for estimating SOC and focusing on the analyzing ampere-hour integral method and extend Kalman filter algorithm,a method combined with ampere-hour integral method and extend Kalman filter algorithm were proposed to estimate SOC.Taking in the voltage and current data of the marked cell and the identified parameter of model,the SOC of the cell was simulated and calculated in the Matlab.The simulation result showed that the proposed algorithm can improve the accuracy of SOC estimation,and has the characteristics of strong anti-interference and convergence.Finally,the active balancing circuit is designed based on the flyback converter,based on the difference of the battery consistency,the balancing strategy was worked out.The balancing circuit and the balancing strategy was simulated in the Simulink of Matlab.The simulation results showed that the balancing circuit and the equalization strategy have the advantages of short balancing time and high equalization efficiency.